Flash-based devices as cold storage is a bad idea.

Photographer here, professional. SDs fail while in use. They’re not 100% reliable for their intended purpose, let alone unintended.

I’ve known loads of photographers that use SD cards as “backups”. And it has a super high failure rate.

Ok, first of all learn rsync or robocopy. But you being on Mac rsync should be your guy (My personal favourite). Those two will only copy the difference between A and B. Waay faster than copying back backup everytime and won’t consume the disk as much.

Now that you know, rsync stuff into the microsd card can now become a daily thing, depending on your usage and how much change you have between sessions.

By sessions I mean whenever you work the data and the progressive difference between backups.

Now, about the long game. I’ve been using on my phones and tablet for at least 2 years swapping movies and music on them every few months and they still work.

I have another one plugged into the work laptop and slapped a VM on it because it was unused and decided to test how long before it breaks. 6 months into the test, 100 or more boots and still holds it.

So in the end I agree with the other comments, it depends a lot on how many times you’ll replace ALL 1TBs on the microsd. That’s what damages it the most, if you edit a few GB every month with rsync or similar you can try.

I guess if you check it periodically, like once a quarter or year, it would be ok. It might not effectively be too different than a HDD since you have to check that periodically too, but more often checks might be warranted due to aformentioed points in this thread about flash data retention and MicroSD reliability.

Since when have microSD cards been considered reliable?

No. SD cards are not reliable.

I heard MicroSDs biggest weakness is the limited writes before it breaks?

I mean if you’re running it in a dashcam yeah, absolutely have to spend the extra few bucks for an endurance rated one.

I heard MicroSDs cannot be without power for a long time.

Nah not anywhere in my list of reasons this would be a bad idea.

I highly recommend against using them on two points

1. They are more fragile and easy to break than they look, especially with age they get so brittle that they will physically break apart even without being mistreated.

2. Their most common way of failing aside from physically breaking apart is silently corrupting data. What you put there won’t match what you get back immediately after being written.

So if you still want to use it for backup I highly recommend ensuring whatever your using for backup can both verify the written data matches the original and alert you the card has failed if it doesn’t and have some way of verifying that the files haven’t been corrupted since then.

That way you can tell which if any of your two copies are good.

Also get it to handle minor corruption if you can like with par files or something so even if both partially fail your still have some ability to recover.

These are good recommendations for any storage media but sd cards and flash drives are just particularly bad at this IME.

Yes, you can encrypt your SD card with disk utility.

I would heavily suggest not doing this. HDDs are significantly more reliable than flash storage when it comes to long-term, power-off data retention. Period. There’s a relatively little-known fact about SSDs and flash storage where they aren’t actually rated to sit around with data on them for all that long. The voltages stored inside of them degrade and the data is slowly lost over time if they aren’t powered on. The enterprise SSDs that I work on are rated for 3 months - as in, set it on a shelf for three months, and after that, if you don’t power it on, it isn’t guaranteed that all of your data will still be there. And this is talking about ultra-redundant, enterprise SAS SSDs. MicroSDs don’t have any of that redundancy. (And yes - this implies that setting a bunch of important flash drives in a safe for ten years is not a great idea. That is true! It’s unlikely that you will experience data loss, but it’s more likely than with an HDD)

Older techies/digital photographers can pull out a drawer with tons of old SD and CF cards, and the truth is most find their data completely readable. I have some from 2000 (ex: a 16mb card - yes, megabytes) that still have old intact WordPerfect and Wordstar files read by my universal reader software. With that said, SD cards were never designed for cold storage. Can you read thousands of anecdotal stories of failure? Yes! However, retention of data on these cards is much greater than a few of the responses here would lead you to believe. Look at any photography subreddit and you’ll see when asked about SD failures that most say none, one, or two out of dozens and dozens, even 100+ cards used. The real-world endurance of high quality flash is pretty damn good. The vast majority of these cards last up to their rated 10 years and beyond. The key is buying from quality manufacturers and not buying their “economy” lines sold in some parts of the world. Never buy generic. But, when dealing with any kind of storage medium - the key word, beyond anything else is: backup.